MI DOT has bike maps by region and we used one to do the Luddington-Luther leg in 2008. It took about 4 hours I think. Longer than it should as one road marked "paved" was soft sand and it was slow and we got lost due to some flooding and closed roads. The Erie Connector route was generally good, though some roads were w/o shoulders and less than nice drivers. We did get lost in Bay City. Be sure to stop in Fairview at the Catamore Zangalotti Flashback Cafe and have "martian nuts". Brown City..home to the first RV is a good stop as well. The ferry ride on the "Badger" is fun..be sure to play Bingo for that ultimate culture experience.
Read days 50-53 at our blog at www.fllt.org/blog/ and link to Michigan under categories. Great time of year to plan a trip. We finished our coast-coast trip in S. Maine at Wells.